Chapter Seven

Atomic Structure

neutrons atoms protons (positive charge )

electrons (negative charge)

7-1 Changing Ideas about Atomic

Structure

7-2 The Quantum Mechanical

Description of Electron in Hydrogen

Atoms

7-3 Electron Configuration of Many-

electron Atoms

7-4 The Periodic Table and Periodic Law

1805 dolton proposed atom theory, proved

exist of atom

1900 electron were discovered

1911 Ruthrford proposed the atomic

nucleus by α-ray scatting

1931 neutron were discovered

7-1.1 The Bohr theory of Hydrogen Atom

Ruthrford’s nuclear model

Figure 7-1: In classical theory: 1.atoms constructed are not stable;

2.the electron would quickly spiral into the nucleus.

3. Not is the line spectra of atoms

Continuous spectrum

Na

Atomic Line Spectra

（ H 、 He 、 Li 、 Na 、 Ba 、 Hg 、 Ne light emission)

In 1913, Niels Bohr(1885-1962), founded Bohr theory by using the work of Planck and Einstein

Quantum of concept emission Atom a copy of energy

absord

quantum

no continuum

Least unit

Physicist Albert Einstein (1879 -1955)

The Photoelectric EffectEinstein used the quantum theory to explain the photoelectric effect :

Each energy packet called photon, is a quantum of energy E=h v

h Planck’s constant = 6.623×10-34J s.

E = hv =

c

h

Photons of high frequency radiation have high energies, whereas photons of lower frequency radiation have lower energy.

（波粒二象性）

7-1.1 The Bohr theory of Hydrogen Atom

Bohr set down the following two postulates to account for:

(1) the stability of the

hydrogen atom (that the atom

exists and its electron does not continuously radiate energy and spiral into the nucleus)

(2) the line spectrum of the atom.

Bohr theory of Hydrogen Atom Bohr assumed that: 1.Energy-level postulate an atom looked something like the solar

system: 1) a nucleus at the center 2) the electron could have only certain

orbits

2

hnL

L 代表电子运动轨道的角动量（ L= p ·r =mv r ）P 是电子轨道运动动量，r 是轨道半径，m 是电子的质量，v 是电子的运动速度。

量子化条件： 电子在任意轨道做圆周运动的角动量 mv r

必须是 的整数倍， n = 1, 2, 3, 2

h

+

n=1

n=2

n=3

r =52.9pm

3) energy levels: an electron in an atom can have only specific energy values, which are called the energy levels of the electron in the atom

En = - (Z2/n2) ×2.180 × 10-18J (for H atom)

Z : 核电荷数

n : 能级数 1, 2, 3, --- ∞

Bohr theory of Hydrogen Atom

n 值越大，表示电子运动轨道离核越远，能量越高。

2. Transitions （跃迁） between energy levels photons are given off or absorbed

when an electron moves from one

orbit to another.

ground state a lower energy state

( if n = 1, is called ground state )

excited state a high energy state

( if n = 2 、 3……, is called ground state)

• Orbit –

• Ground state –

Ground state

Excited stateEnergy of emitted photon

ΔE = Ei - Ef = hvEi a higher energy level (initial energy level)

Ef a lower energy level (final energy level )

In 1885, J.J. Balmer showed that the wavel

engths, λ, in the visible spectrum of hydrog

en could be reproduced by a simple formula.

1 1 1 --- = 1.097 × 107m-1 ( ---- - -----) λ 2 2 n 2

postulate from level n = 4 to level n = 2 light of wavelength 486 nm (blue green ) is emitted

Hydrogen atom spectra

Visible lines in H atom

spectrum are called the

BALMER series.

High EHigh EShort Short High High

Low ELow ELong Long Low Low

En

erg

y

Ultra VioletLyman

InfraredPaschen

VisibleBalmer

65

3

2

1

4

n

Bohr’s theorySuccessful

1.established the concept of atomic energy levels (atomic orbit)

2. explaining the spectrum of hydrogen

Unsuccessful

1. atomic orbit is fastness

2. can’t explain minuteness the spectrum of hydrogen atom

Louis-Victor de Broglie, (1892 -1987, France)

In 1929, he was awarded the Nobel Prize for Physics for his research on quantum theory and his discovery of the wave nature of electrons.

He showed that the wavelength of moving particles is equal to Planck's constant divided by the momentum.

7-1.2 De Broglie Waves (Matter Waves)

Mass: >> h ,

Particle:

m wave properties ignored

<<h ，m

wave properties

p

h

m

h

can not ignored

is short

（ 7-4 ）

[ 例 7 － 1] 分别计算 m=2.5×10-2kg ， v = 300m·s-1 的子弹 和 me=9.1×10-31kg v =1.5×106 m·s-1 的电子的 波长，并加以比较。

解： 按（ 7-4 ）式，子弹的波长为：

电子的波长为：

计算结果表明，子弹的波长很短，完全可以不予考虑。

)(108.8)(108.8300105.2

10626.6 23352

34

pmm

)(500105.1101.9

10626.6631

34

pm

1927 年美国物理学家 Davisson C 和 Germer L 根据电子的波长 与 X 射线波长相近，用电子束代替 X 射线，用镍晶体薄层 作为光栅进行衍射实验，得到与 X 射线衍射类似的图像， 证实了电子的波动性。

电子的波粒二象性（ Davisson 和 Germer 实验 ）

X-diffracted electron diffracted

7-1.3 The Heisenberg Uncertainty principle

1927 ,He recognized :

no experimental method can be devised that will measure simultaneously the precise position(x) as well us the momentum (mv) of an object.

Heisenberg German physicist (1901-1971)

Uncertainty principle formula

Δp uncertainty of the momentum Δx uncertainty of the position h Planck's constant

ν4

4

m

hx

hxp

或

The more precisely one knows Δp, the less precisely Δx is known, and vice versa.

•ExampleSuppose Δx=1.0 ×10- 4 m for a substance with

mass of 0.01kg

)(103.5

100.1100.114.34

10626.6

4v

129

42

34

sm

xm

h

In hydrogen atom, for an electron, v =106m/s ,

suppose Δx=1.0 ×10- 10 m,

)(108.5

101011.914.34

10626.6

4v

15

1031

34

sm

xm

h

电子速度的不准确量与其速度本身十分接近

( 中文 p148_)

Quantum or Wave MechanicsQuantum or Wave Mechanics

Schrodinger applied idea of e-

behaving as a wave to the problem of electrons in atoms.

E. SchrodingerE. Schrodinger1887-1961 1887-1961 1933 received the Nobel Prize

0)(8

2

2

2

2

2

2

2

2

VEh

m

zyx

E the total energy V the potential energy m a particle in terms of its massx y z respect to its position in three dimensions

7-1.4 Schrődinger Equation (wave function)

0)(8

2

2

2

2

2

2

2

2

VEh

m

zyx

Solution to WAVE EQUATION gives set of

mathematical expressions called

WAVE FUNCTIONS ψ (psi)

wave function ψ has an amplitude （振幅） at each position in space (just as for a water wave or a classical electromagnetic wave).

ψ is a function of is a function of distancedistance and and two angles. two angles. ———— Ψ(r,θ,φ) 、

ψ does does NOT describeNOT describe the the exact locationexact location of the of the electron.electron.

For 1 electron, For 1 electron, ψ corresponds to an corresponds to an ORBITALORBITAL

— — the region of space within which an the region of space within which an

electron is found.electron is found.

7-2.1 Wave Function, Atomic Orbital and Electron Cloud

7-2.2 Atomic Orbital ____ Quantum Numbers

n the principal quantum number l the angular momentum quantum number m the magnetic quantum number.

they will be used to describe atomic orbitals and to label electrons that reside in them.

1. Principal quantum number (n): Shell K L M N . . .

n 1 2 3 4 . . .

As n increases, the orbitals extend farther from the nucleus,average position of an electron in these orbitals is farther from the nucleus

Energies: K<L<M<N<O< … 1<2< 3< 4< 5 < …

2. Angular momentum quantum number (l ) Within each shell of quantum number n ,

there are n different kinds of orbital, each with a distinctive shape, denoted by the

l quantum number. subshell s p d f g . . . l 0 1 2 3 4 . . .(n-l) Energies: s<p < d < f < g…

3. Magnetic quantum number (m): A subshell has the same shape, but a different

orientation, or direction, in space.

m = (2 l + 1) or

Each orbital of a particular subshell (no matter how it is oriented in space) has the same energy.

Example: p orbit have 3 different orientation

p x. p y p z

... 3 2 1 0 l

About Quantum Numbers —— Orbital

An atomic orbital is defined by 3 quantum numbersAn atomic orbital is defined by 3 quantum numbers::

Electrons are arranged in Electrons are arranged in shellsshells and and subshells subshells of of RBITALS RBITALS ..

n n shell shell

l l subshell subshell

mm designates an orbital within a subshell designates an orbital within a subshell

nn ll m

Table 7-1: The allowed sets of quantum numbers for atomic orbitals

4. Spin quantum number (ms) :

ms the spin quantum number refers to a magnetic property of electrons called spin.

Values for the spin quantum number are +1/2 and –1/2.

A fourth quantum number

Note: n. l. m. ms

they will be used to describe electrons that reside in them

QUANTUMNUMBERS

1. Which of the following is not a valid set( 有效的组合 ) of four quantum numbers to describe an electron in an atom? (1) 1, 0, 0, +½ (2) 2, 1, 1, +½ (3) 2, 0, 0, –½ (4) 1, 1, 0, +½

2. The energy of an orbital in a many-electron atom depends on (1) the value of n only (2) the value of l only (3) the values of n and l (4) the values of n, l, and m

30.0.

).(.)(.)..(..

mlrlnrmln YR

).(.)(.)..(.. mlrlnrmln YR

Radial wave function angular

wave function

7-2.3 Sizes and Shapes of Atomic Orbitals

Spherical coordinates

x = r sin cos

y = r sin sin

z = r cos

Shapes of the orbitals

Shapes of the orbitals for:

(a) an s subshell

(b) a p subsell

(c) a d subshell ?

如：氢原子的角度部分

【 s 轨道】

Ys 是一常数与 ( 无关，半径为 :

【 pz 轨道】

4

1

4

1),( sY

cos4

3),(

zpY

节面：当 cos 时时时时

时时时时时时时时时时时 Pz 平面时时时时

30

60

0

90x,y

z

+

－

30°

60°θ

节面：当 θ = 90° cosθ= 0 Ｙ =0 时

0.489- 0.423- 0.244- 0 0.244 0.423 0.489 Y

1- 0.866- 0.5- 0 0.5 0.866 1 cos

180 150 120 90 60 30 0

Pz

波函数的角度分布图

由图可知，原子轨道的角度分布图有正负之分，这对于讨论分子的化学键及对称性十分重要。同样地，可以画出其它原子轨道的角度分布图。

The Probability Function (ψ2)

—— Electron Cloud ψ2 is related to the probability per unit volume such that the product of ψ 2 and a small volume (called a volume element) yields the probability of finding the electron within that volume.

1. Electron Cloud

The total probability of locating the electron in a given volume (for example, around the nucleus of an atom) is then given by the sum of all the products of ψ2 and the corresponding volume elements.

2px2pz

f orbitals

).(.)(.)..(.. mlrlnrmln YR

|Ψn,l,m(r,θ,φ) |2 = R2n,l(r) • Y2

l,m(θ,φ)

Probability density

电子云的径向分布图

P=|Ψ|2 • dV

Probability

几率 (dP)= 几率密度 (|ψ|2)× 体积 (dV)

电子云的径向分布图考虑离核距离为 r，厚度为 dr的薄层球壳内发现电子的几率 . 1s 球壳微体积： dV = 4πr2dr

D(r) =4πr2dr •R2(r)----- 壳层几率（球壳层内发现电子的几率）

P=|Ψ|2 • dV= |Ψ|2 •4πr2dr

=4πr2dr •R2(r) • Y2

l,m(θ,φ)

Probability

= D(r) • Y2l,m(θ,φ)

Radial distribution

function diagram

Angular distribution

function diagram

离核越近： r 值越小，体积越小， |ψ|2 越大， D(r) 不是最大，离核越远： r 值越大，体积越大， |ψ|2 越小， D(r) 亦不是最大， 在 ao 处： |ψ|2 不是最大的 , 但体积较大，使 D(r) 可达最大。

P= |Ψ|2 •4πr2dr

ao=52.9pm 处。当 r=2ao 时， D(r)=0, 出现第一个节面。当 r=4ao 时， D(r) 又出现最大值 , 此即 2s 电子云

当 r=2ao 时， D(r)=0, 出现第一个节面。当 r=4ao 时， D(r) 又出现最大值 , 此即 2s 电子云

电子云的径向分布图 峰数＝ n-l

7-3 Electron Configuration of Many-electron Atoms

1. An electron configuration describes the arrangement of electrons in the subshells of an atom.

2. The chemical properties of elements are related to these configurations.

3. The four quantum numbers n, l, m, and ms

enable us to label completely an electron in any orbital in any atom.

Order of filling orbitals

Generally, the energy of an orbital depends

on the quantum n and l .

E1s E2sE 2p E3sE3p E3d E4sE 4p E 4d E4f E5s…

1s 2s2p 3s3p 4s3d4p 5s4d5p 6s4f5d6p 7s…

Why? This phenomenon can be explained by shielding

effect (screening effect) and penetrating effect.

1. The shielding effect is that it reduces the electrostatic attraction between protons in the nucleus and the electron in outside orbital.

2. The penetrating effect of an electron can

decrease the energy of orbital.

1s

D(r)

r

2s

3s

D(r)

r

3d 3p

3s

图 1 l 相同， n 不同时的比较

图 2 n 相同， l 不同时的比较

从上图可以看出： （ 1 ） l 相同， n 不同 : 1s<2s<3s . n 增大时，电子离核的距离 （主峰）将增加。 （ 2 ） n 相同， l 不同 3s<3p<3d. l 值大，峰个数减少。 l 值小，电子在核附近出现的机会（钻穿峰）较多。

The penetrating effect

钻穿效应 : 外层电子向内层穿透，导致内层电子对它的屏蔽作用减弱的效应叫钻穿效应

(3) n,l 都不同时，将出现能级交错 :

4s<3d<4p

为什么 2s 价电子比 2p 价电子受到较小的屏蔽 ?

Question

2s 电子云径向分布曲线除主峰外 , 还有一个距核更近的小峰 . 这暗示 , 部分电子云钻至离核更近的空间 , 从而部分回避了其他电子的屏蔽 .

The electron fill law1.principle of energy levels lowest Electrons in an atom occupy the lowest possible

energy levels, or orbitals. 2.The Pauli exclusion principle: No two electrons in the same atom can have the s

ame set of four quantum numbers. 3.Hund's rule: Every orbital in a subshell is singly occupied (fill

ed) with one electron before any one orbital is doubly occupied, and all electrons in singly occupied orbitals have the same spin;

All of the electrons in an atom reside in the lowest energy orbitals possible as long as permission of Pauli exclusion principle .The electrons filling order is ： 1s, 2s2p, 3s3p, 4s3d4p, 5s4d5p, 6s4f5d6p, 7s5f……

1.principle of energy levels lowest

1s

2s2p

3s3p

4s4p

3d

5s5p 4d

6s6p 5d 4f

2. Pauli Exclusion Principle (2n2)

The Pauli exclusion principle states that no

two electrons in an atom can have the same

set of four quantum numbers: n l m and ms.

Thus, for two electrons to occupy the same

orbital, one must have ms = + ½ and the

other must have ms = – ½.• electrons with the same spin keep as far apart as possible• electrons of opposite spin may occupy the same orbital

3. Hund’s rule( 洪特规则 )

This rule states that for orbitals with the same energy, the lowest energy is attained when the number of electrons with the same spin is maximized.

而不是是

按洪特规则的基态电子构型N

1s

2s 2p

1s

2s 2p

Ô ×ÓÐòÊýΪ7

Example Boron(atomic number =5) B 1s22s2 2p1

Nitrogen (atomic number =7) N 1s22s2 2p3

Magnesium (atomic number =12) Mg 1s22s2 2p63s2

or [Ne]3s2

Chromium (atomic number =24) Copper (atomic number =29) ? Lanthanum (atomic number =57)

According to Hund’s rule and Pauli exclusion principle, we can writing the electron configurations for other elements. Example: chromium (Z = 24) [Ar]4s13d 5 or [Ar]4s23d4

half-filled (s1 p3 d5)Subshells completely empty(s0p0d0) stability completely filled (s2 p6 d10)

11 s

value of nvalue of l

no. ofelectrons

SPECTROSCOPIC NOTATIONfor H, atomic number = 1

电子层结构式要与原子的电子排布式区别开，以 29号元素铜为例：

电 子 排 布 式： 29Cu: 1s2 2s2 2p6 3s2 3p6 4s1 3d10

电子层结构式： 29Cu: 1s2 2s2 2p6 3s2 3p6 3d10 4s1

（或电子构型式 )

7- 4 The Periodic Table and Periodic Law Then in 1869, Russian chemist Dimitri Mendeleev (1834-1907) proposed arranging elements by atomic weights and properties (Lothar Meyer independently reached similar conclusion but published results after Mendeleev).  Mendeleev's periodic table of 1869 contained 17 columns with two partial periods of seven elements each (Li-F & Na-Cl) followed by two nearly complete periods (K-Br & Rb-I).

7- 4 The Periodic Table and Periodic Law

The modem Periodic Table consists of

7 horizontal( 水平 ) rows of elements (often

referred to as periods or series) and

32 vertical （垂直） columns of elements

(referred to as families or groups).

维尔纳长式周期表

114 116 118

1

2

3

4

5

6

7 钅钅 钅 钅喜 波 黑 麦卢 钅杜钅

镧系

锕系

钫 镭

铌

钽

银

金

镉

汞

铟

铊

锡

铅

锑

铋

碲

钋 砹 氡

氙碘

镧 铈 镨 钕 钷 钐 铕 钆 铽 镝 钬 铒 铥 镱 镥

锕 钍 镤 铀 镎 钚 镅 锔 锫 锎 锿 镄 锘 铹钔

铷

铯

锶

钡

钇 锆

铪

钼

钨

锝

铼

钌 铑 钯

锇 铱 铂

氢

锂

氦

铍 硼 碳 氮 氧 氟 氖

钠 镁 铝 硅 磷 硫 氯 氩

钾 钙 钪 钛 钒 铬 锰 铁 钴 镍 铜 锌 镓 锗 砷 硒 溴 氪

Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe

Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn

IB

IA

IIA IIIA IVA VA VIA VIIA

VIII IIBIIIB IVB VB VIB VIIB

Rf Db Sg Bh Hs MtUun Uuu UubAc-Lr

La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

H He

Li Be B C N O F Ne

Na Mg Al Si P ClS Ar

K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr

Rb

Cs

Fr

Sr

Ba

Ra

Y

LaLu-

1 2

3 4 5 6 7 8 9 10

11 12 13 14 15 16 17 18

19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

55 56

57 58 59 60 61 62 63 64 65 66 67 68 69 70 71

72 73 74 75 76 77 78 79 80 81 82 83 84 85 86

87 88

89 90 91 92 93 94 95 96 97 98 99 100 101 102 103

104 105 106 107 108 109 110 111 112

57

89103-

-71

periodsshort period

First (2 element)secondthird

long periods

(8 element)(8 element)

fourth

fifth

18 elements

18 elements

sixth 32 elements

seventh 32 elements

periods or seriesThe first short period contains

two elements hydrogen (H)and helium （ He). The second short period contains

eight elements, beginning with lithium (Li) and ending with neon (Ne).

The third short period also contains

eight elements, beginning with sodium (Na)and ending with argon (Ar).

The two long periods, The fourth period and the fifth period

are two long periods, each of which contains 18 elements.

The fourth period includes the elements from potassium (K)through krypton (kr).

Within this period are the elements from scandium (Sc)through copper(Cu), which are known as the first transition series.

The fifth period is begins with rubidium (Rb)and ends with xenon (Xe).

Within this period are the elements yttrium (Y) through silver (Ag),which comprise the second transition series.

The sixth period

The sixth period, beginning with cesium (Cs)and ending with radon (Rn),contains 32 elements.

The third transition series, made up of lanthanum (La)and the elements hafnium (Hf)through gold (Au)

The sixth periodThe third transition series is split:

between lanthanum and hafnium is a series of 14 elements, cerium (Ce) through lutetium (Lu),called the first inner transition series, or the lanthanide series or the

rare earth elements.

The seventh period

The seventh period extends from francium through element number 118.

However, no elements after element 109 have been characterized.

The known elements in this period include a part of the fourth transition series (actinium, and elements 104 through 109).

Electronic Structure and the Periodic

Law the periodicity with respect to the

number of valence electrons;

valence electrons that is, electrons in the outermost shell.

the Periodic Table is simply an arrangement of atoms that puts elements with the same number of valence electrons in the same group.

表：基态电中性原子的电子组态

1 氢 H 1s1

2 氦 He 1s2

3 锂 Li [He] 2s1

4 铍 Be [He] 2s2

5硼 B [He] 2s22p1

6 碳 C [He] 2s22p2

7 氮 N [He] 2s22p3

8 氧 O [He] 2s22p4

9 氟 F [He] 2s22p5

10氖 Ne 1s2 2s22p6

11钠 Na [Ne] 3s1

12镁Mg [Ne] 3s2

13铝 Al [Ne] 3s23p1

14硅 Si [Ne] 3s23p2

15磷 P [Ne] 3s23p3 16硫 S [Ne] 3s23p4 17氯 Cl [Ne] 3s23p5 18氩 Ar 1s22s22p63s23p6 19钾 K [Ar] 4s1

20钙 Ca [Ar] 4s2

21钪 Sc [Ar] 3d14s2

22钛 Ti [Ar] 3d24s2

23钒 V [Ar] 3d34s2

24铬 Cr* [Ar] 3d54s1

25锰Mn [Ar] 3d54s2

26铁 Fe [Ar] 3d64s2

27钴 Co [Ar] 3d74s2

28 镍 Ni [Ar] 3d84s2

不符合构造原理

价层电子 价电子层 “电子仁”或“电子实”

1-48号元素的核外电子层结构1 H 1s1 17 Cl [Ne]3s23p5 33 As [Ar]3d104s24

p3

2 He 1s2 18 Ar [Ne]3s23p6 34 Se [Ar]3d104s24p4

3 Li [He]2s1 19 K [Ar]4s1 35 Br [Ar]3d104s24p5

4 Be [He]2s2 20 Ca [Ar]4s2 36 Kr [Ar]3d104s24p6

5 B [He]2s22p1

21 Sc [Ar]3d14s2 37 Rb [Kr]5s1

6 C [He]2s22p2

22 Ti [Ar]3d24s2 38 Sr [Kr]5s2

7 N [He]2s22p3

23 V [Ar]3d34s2 39 Y [Kr]4d15s2

8 O [He]2s22p4

24 Cr [Ar]3d54s1 40 Zr [Kr]4d25s2

9 F [He]2s22p5

25 Mn [Ar]3d54s2 41 Nb [Kr]4d45s1

10 Ne [He]2s22p6

26 Fe [Ar]3d64s2 42 Mo [Kr]4d55s1

11 Na [Ne]3s1 27 Co [Ar]3d74s2 43 Tc [Kr]4d55s2

12 Mg [Ne]3s2 28 Ni [Ar]3d84s2 44 Ru [Kr]4d75s1

13 Al [Ne]3s23p1

29 Cu [Ar]3d104s1 45 Rh [Kr]4d85s1

14 Si [Ne]3s23p2

30 Zn [Ar]3d104s2 46 Pd [Kr]4d10

15 P [Ne]3s23p3

31 Ga [Ar]3d104s24p1

47 Ag [Kr]4d105s1

16 S [Ne]3s23p4

32 Ge [Ar]3d104s24p2

48 Cd [Kr]4d105s2

families or groups1. Elements in any one group have the same

number of electrons in their outermost shell2. The similarity in chemical properties among

elements of the same group occurs because they have the same numbers of valence electrons

3. The number of electrons in the valence shell of an atom determines its chemical properties.

4. It is the loss, gain, or sharing of valence electrons that determines how elements react.

families or groups 1. A number of groups

= electron number of outmost shell

= greatest oxidation number

Example: 17Cl 15P

2. B number of groups

=lose electron number [(n-1)d+ns] (except B)Ⅷ =greatest oxidation number(but it can be

changed )

Example: Cr +2, +3, +6

Mn +2 ,+3,+4,+6,+7

Electronegativity The electronegativity of an atom is a meas

ure of the ability of an atom to draw bonding electrons to itself when chemically combined with another atom

In general, electronegativity increases in any row of the periodic table from left to right, and it decreases in going from the top of a column to the bottom.

电负性的应用1．判断元素的金属性和非金属性 金属性元素的电负性一般在 2.0 以下，非金属性性元素一般在 2.0 以上。电负性最大的元素是位于右上方的 F ，电负性最小的元素是位于左下方的 Fr （ Fr 是放射性元素）

2．估计化学键的类型 在化合物中，可以根据电负性的差值大小，估计化学键的类型。 电负性差越大，离子性越强，一般说来，电负性差大于 1.7 时，可认为是离子键，小于 1.7 时为共价键。

原子半径及其周期性变化

原子半径 : 有三种不同的定义

（ 1 ）共价半径 : 同种元素的两原子以共价单键相连时 ,两原子核间距离的一半叫共价半径 .

（ 2 ）金属半径 : 金属元素的两原子以密堆积方式 (金属键 )结合成金属晶体时 ,两原子核间距离的一半叫金属半径 .

（ 3）范氏半径 : 同种元素的两原子不能以共价键相连 ,只靠分子间力作用时 ,两原子核间距离的一半叫范德华半径 .

1 、原子半径及其变化规律

2 、主族元素原子半径的变化规律主族元素 :(1)同周期 从左到右

逐渐减小 .但到希有气体元素时又有增大 ,原因是半径定义不同 .

(2)同一族 从上到下逐渐增大 .从左到右 ,核电荷增加是主要因素 ,但从上到下 ,电子层增加是主要因素 .

副族元素原子半径的变化规律副族元素 :(1)同周期 从左到右逐渐减小 .但减小幅度不如主

族元素 ,这是由于最后一个电子是填在 (n-1)层 d轨道上对核电荷的抵消作用造成的 .

(2)同一族 从上到下逐渐增大。但增加幅度较小 ,甚至第五、第六周期基本没有增加 ,这是由于镧系收缩的原因造成的 .